1. Field
This disclosure generally relates to RFID (Radio Frequency Identification) devices and methods useful in backscattering of wireless communications signals.
2. Description of the Related Art
The automatic data collection (ADC) field is generally directed to the use of devices and methods for automatically capturing data typically encoded in media such as a tag or other data carrier carried by the item to which the data relates. A variety of ADC devices and ADC media are ubiquitous and well known.
For example, a data carrier may take the form of a radio-frequency identification (RFID) device, which may have the form of a tag, card, case, or other medium. Such are commonly referred to collectively as RFID tags without regard to particular form factor. RFID devices typically include an RFID substrate carrying a circuitry such as a semiconductor device including memory and one or more conductive traces that form an antenna.
Typically, RFID devices act as transponders, providing information stored in the semiconductor device in response to an interrogation signal received at the antenna from a reader or interrogator. The interrogation signal typically takes the form of a radio-frequency (RF) carrier wave signal without, or without, encoded information (e.g., modulated). The information may include a unique identifier of the RFID device, such as a unique serial number (e.g., alpha-numeric), and/or information (e.g., account, manufacturer, model, style, size, weight, price, color, etc.) about the item to which the RFID device is attached or otherwise associated.
Some RFID devices include security measures, such as requiring passwords to access data and/or employing encryption. Many RFID devices also permit information to be written or stored in the semiconductor memory via an RF signal. As used herein, radio-frequency communications include communications in any frequency band or range suitable for wireless communications, including those commonly referred to as the radio wavelength and the microwave wavelength portions of the electromagnetic spectrum.
RFID devices that include a discrete power source, for example a battery, are commonly referred to as active devices. RFID devices that rely on an RF signal to derive power are commonly referred to as passive devices, which typically employ modulation backscatter techniques. Some RFID devices may employ both active and passive power sources.
Identification of passive RFID devices generally depends on RF energy produced by a reader or interrogator arriving at the RFID device, which backscatters modulated RF energy to the interrogator. In general, lower frequencies can penetrate objects better than higher frequencies, but higher frequencies can carry more data than lower frequencies. In addition, multiple protocols exist for use with RFID devices. These protocols may specify, among other things, particular frequencies, frequency ranges, modulation schemes, security schemes, and data formats. Conventional approaches employ multiple RFID devices, each RFID device using a frequency band and protocol suited to a particular application.
Currently, there are passive RFID tags with multiple antennas that receive interrogation signals from a reader or interrogator via all the antennas. The RF voltage developed on the antennas is converted to DC voltage, thereby generating enough power for the RFID tag to power up and transmit a response. Transmitting the response takes the form of backscattering modulated interrogation signals via all the antennas. The RFID tag does not receive power via the antennas during backscattering, hence the power at the RFID tag drastically decreases. This disadvantageously reduces the time during which the RFID tag can continue functioning without receiving additional power via the antennas, as well as reducing the range of the RFID tag.
It is therefore desirable to have a passive or partially passive RFID device and method for backscattering modulated signals while simultaneously ensuring that the RFID device receives sufficient power to continue functioning with maximum range.